High Quality Content by WIKIPEDIA articles! Xenacanthidae is a
family of prehistoric sharks in the order Xenacanthida. Sharks
(superorder Selachimorpha) are a type of fish with a full
cartilaginous skeleton and a highly streamlined body. The earliest
known sharks date from more than 420 million years ago, before the
time of the dinosaurs. Since that time, sharks have diversified
into 440 species, ranging in size from the small dwarf
lanternshark, Etmopterus perryi, a deep sea species of only 17
centimetres (6.7 in) in length, to the whale shark, Rhincodon
typus, the largest fish, which reaches approximately 12 metres (39
ft 4 in) and which feeds only on plankton, squid, and small fish
through filter feeding.